John O'Brien, 53, was an inmate at Dorchester Penitentiary when he died at a Moncton hospital on Thursday, Correctional Service Canada officials say. (Archives)

A violent sex offender known as the Motorcycle Rapist, who was released to a halfway house in Saint John last spring, died in custody on Thursday, Correctional Service Canada confirmed on Monday.

John Arthur O'Brien, 53, who terrorized Halifax in the late 1980s, was an inmate at Dorchester Penitentiary at the time of his death, CSC spokesperson Nadine Boucher said.

His statutory release had been suspended, she told CBC News, declining to divulge any details about when or why.

O'Brien died at a Moncton hospital from unspecified injuries, Boucher said.

"As in all cases involving the death of an inmate, the police and the coroner have been notified, and Correctional Service Canada will review the circumstances of the incident," she said.

RCMP Staff Sgt. James Bates says O'Brien had serious internal injuries.

The RCMP is investigating because it was a sudden death, but no foul play is suspected, Bates said.

Dorchester is a medium-security prison for about 400 male offenders.

'Potential to be very dangerous'

O'Brien had been serving a sentence of 37 years and nine months for sexually assaulting eight women at knife-point while wearing a motorcycle helmet, as well as other offences.

O'Brien, who was convicted in 1989, had reached his statutory release date after serving two-thirds of his sentence and could not be held any longer.

But the National Parole Board had expressed concerns, noting O'Brien's most recent psychological assessment concluded his risk of sexual recidivism was in the "high end of the moderate range" and his risk for general violence was in the "moderate range."

"You have the potential to to be very dangerous," his parole documents stated.

The Saint John Police Force had opposed O'Brien being placed at a halfway house in the city and several citizens had expressed concerns. An online petition was started, calling for him to be removed from the city or for his parole to be revoked.

The parole board had attached several conditions to O'Brien's release. He was ordered to be under close supervision and not allowed any leave privileges.

O'Brien was also ordered to stay away from all forms of pornography, abstain from alcohol and drugs, report all relationships with women and stay away from his victims, their families and known criminals.

O'Brien's criminal record dated back to 1976. He was released several times on parole, only to reoffend.

In 1984, he was granted day parole, which was revoked.

He was granted statutory release in 1985, which was suspended for violence.

In 1988, he was granted day parole and then qualified for full parole after six months without an incident. It was while he was on full parole that he committed the Halifax rapes.

His next of kin have been notified of his death.